Autonomic NS (micturition and defecation)

Question 1

define GSE, GVE, and GSA/GVA

Answer 1

GSE: general somatic efferent; innervation of skeletal muscle

GVE: general visceral efferent; innervation of smooth muscle via autonomic nervous system

GSA/GVA: sensory

Question 2

give the neurotransmitter, NMJ receptor, and target tissue receptor used by sympathetic pathways and parasympathetic pathways

Answer 2

sympathetic: use norepinephrine, but release ACh at NMJ; will release the norepinephrine at adrenergic receptors in target tissues

parasympathetic: use acetylcholine both at NMJ and at muscarinic receptors in target tissues

Question 3

what are the 2 types of cholinergic receptors, what neurotransmitter do they use, and where are they located?

Answer 3

nicotinic receptors in skeletal muscle and muscarinic receptors in smooth muscle; use acetylcholine

Question 4

what are the 2 types of adrenergic receptors and what neurotransmitter do they use?

Answer 4

alpha and beta; use norepinephrine

Question 5

describe the anatomy of the bladder (3)

Answer 5

1. bladder/detrusor muscle: smooth muscle
2. internal urethral sphincter: smooth muscle
3. external urethral sphincter/urethralis muscle: skeletal muscle

Question 6

describe somatic innervation of the bladder (3)

Answer 6

1. sacral spinal cord segments (S1-S3 in dog and cat) give rise to the pudendal nerve
2. contraction of the external urethral sphincter is accomplished via nicotinic cholinergic receptors
3. acetylcholine is the neurotransmitter responsible!!

Question 6

what do the sympathetic and somatic systems do for pee? what does the parasympathetic do?

Answer 6

Somatic and Sympathetic = Storage
Parasympathetic = Pee

Question 6

describe the sympathetic innervation of the bladder (5)

Answer 6

1. L1-L4/5 spinal cord segments give rise to the hypogastric nerve
2. sympathetic innervation directly inhibits contract of bladder, allowing expansion/filling via BETA receptors on bladder/detrusor muscle
3. sympathetic innervation inhibits parasympathetic contraction of bladder via alpha-2 receptors
4. sympathetic innervation allows for contraction of the internal urethral sphincter via alpha-2 adrenoreceptors
5. norepinephrine!! is the neurotransmitter responsible!

Question 7

describe parasympathetic innervation of the bladder (3)

Answer 7

1. sacral spinal cord segments (S1-S3 in dog and cat) give rise to the pelvic nerve
2. contraction of the bladder is accomplished via muscarinic cholinergic receptors
3. acetylcholine is the neurotransmitter responsible!!

Question 8

how do we know the bladder is full? (describe sensory innervation of the bladder) (4)

Answer 8

1. mechanoreceptors in the bladder wall detect stretch
2. these mechanoreceptors predominantly send info via the pelvic nerve
3. this info can go to the local LMN of micturition for reflex activity OR
4. can go cranial to the brain, to the UMN in the brainstem (pontine micturition center) and to the cerebrum for conscious recognition

Question 9

describe storage of urine

Answer 9

1. bladder begins to fill with urine, is sensed by stretch receptors via the GVA in the pelvic nerve
2. information ascends via the spinothalamic tracts to the PMC and cerebral cortex
3. UMN descend via reticulospinal tracts to
   3a. inhibit parasympathetic muscarininc cholinergic pelvic nerve and allow the bladder to relax
   3b. facilitate sympathetic adrenergic hypogastric nerve to allow bladder relaxation and internal urethral sphincter contraction
   3c. facilitate somatic pudendal nerve to constrict the external urethral sphincter (which is under voluntary control so you can choose not to pee)

Question 10

describe peeing (voiding bladder)

Answer 10

1. bladder stretch exceeds threshold (sensed by GVA in pelvic nerve)
2. information ascends via spinothalamic tracts to PMC and cerebral cortex
3. UMN descend via reticulospinal tracts to
   3a. facilitate parasympathetic muscarinic cholinergic to allow bladder contraction
   3b. inhibit sympathetic adrenergic hypogastric nerve to allow internal sphincter relaxation and stop bladder relaxation
   3c. inhibit somatic pudendal nerve to relax the external urethral sphincter

Question 11

how common are cerebral and cerebellar lesions that affect micurition?

Answer 11

cerebrum: uncommon; cerebrum is in charge of behavior so would only expect inappropriate urination (cat outside of litterbox, dog in house)

cerebellar: rare; cerebellum has an inhibitory effect on micturition, so would see increased frequency of urination

Question 12

describe LMN bladder signs (6)

Answer 12

1. caused by a lesion of sacral segments of nerves (sacral segments in L5-L6 vertebral bodies); usually accompanied by LMN signs in pelvic limbs; S1-S3 also commonly seen with L1-L4 lesion; can affect in the spinal cord or peripherally, if peripheral will also see concurrent sciatic nerve problems too bc L7 nerve root also affected
2. no perception of bladder filling due to lack of GVA pelvic nerve
3. large flaccid bladder due to lack of GVE pelvic nerve
4. decreased external urethral sphincter tone due to lack of GSE pudendal nerve; patient dribbles urine
5. should be easy to express but since flaccid may slip right out of hand and actually be hard to pin down to express
6. decreased to absent anal tone, perineal reflex, +/- tail tone

Question 13

how is a UMN bladder accomplished? describe how this relates to UMN signs in limbs

Answer 13

1. lesions from brainstem to L7
2. most commonly from T3-L3
3. bladder is like a 5th limb so UMN bladder will have increased tone, and voluntary micturition ability mirrors voluntary motor ability in limbs

Question 14

describe UMN bladder signs (7)

Answer 14

1. UMN weakness of pelvic limbs will be observed, with normal to increased tone and reflexes
2. no voluntary micturition
3. large turgid bladder
4. increased urethral tone due to lack of descending inhibition to pudendal nerve (on external urethral sphincter)
5. +/- hypogastric nerve effected increasing internal urethral sphincter tone too
6. bladder difficult to manually express
7. normal anal tone and perineal reflex

Question 15

BROADLY describe treatment of neurological signs resulting in issues with micturition (2)

Answer 15

1. if possible, treat underlying neuro cause (duh)
2. if not possible then manage the condition with bladder expression/catheterization and drugs!

Question 16

what is the goal of LMN incontinence treatment?

Answer 16

1. increase contraction and tone of bladder via increasing muscarinic acetylcholine receptors via bethanechol
2. increase sphincter tone: can increase internal sphincter tone by increasing alpha receptors via phenylpropanolamine (can’t really increase external sphincter tone)

Question 17

describe bethanechol as treatment of LMN incontinence (4)

Answer 17

1. parasympathomimetic (mimics PS NS)
2. directly stimulates muscarinic acetylcholine receptors
3. leads to increased bladder tone and contraction
4. side effects are SLUD: salivation, lacrimation, urination, defecation

Question 18

describe phenylpranolamine as treatment of LMN incontinence (4)

Answer 18

1. sympathomimetic/alpha agonist
2. directly stimulates alpha adrenergic receptors (and to a lesser degree also beta receptors)
3. leads to increased urethral sphincter tone
4. potential problems if weakened bladder can’t contract against increased sphincter tone

Question 19

describe UMN incontinence treatment

Answer 19

1. decrease internal urethral sphincter tone (we have the best drugs for this)
2. decrease external urethral sphincter tone? (hard to do)
3. increase bladder contraction with bethanechol? (if you must)

Question 20

how do you decrease internal urethral sphincter tone for treatment of UMN incontinence? (generally and then 3)

Answer 20

want to decrease alpha receptors via
1. prazosin: sympatholytic/alpha antagonist that relaxes internal urethral sphincter
2. diazepam: causes global relaxation of skeletal muscles
3. benzodiazepine: facilitates the inhibitor neurotransmitter GABA to cause skeletal muscle relaxation but does’t always work and has the side effect of sedation